(September 2003) The impact of the world’s 6.3 billion people on the environment is unprecedented. Humans had a negligible effect on the environment 3,000 years ago when fewer than 100 million people lived on Earth, but by the early 21st century, we have altered more than one-third of Earth’s ice-free surface and threatened the existence of many plant and animal species. These changes also pose threats to our well-being. The burning of gas, coal, and oil, for example, is increasing concentrations of carbon dioxide in the atmosphere, altering the global climate and affecting human health.

The number of people is just one factor driving environmental change. Other demographic factors also cause change. Where people live and the rate of population growth increase the demand for natural resources such as water and fossil fuels, adding pressure on environmental systems such as watersheds and rainforests. The relative proportions of children, persons of working age, and elderly within a population have repercussions for future population growth, health risks, and use of services such as public transportation.

Other forces, such as public policies, technological developments, and culture, can ease or worsen the pressures that these demographic factors place on society and the environment. One example is the growth of cities throughout the world. This urban growth brings changes in lifestyles, consumption patterns, infrastructure development, and waste production.

This Population Bulletin highlights the results of research, community projects, and public policies to examine three critical questions about population, health, and environment relationships. First, what is the nature of these relationships? Second, how do these relationships affect human well-being and the environment? And finally, what can researchers, local communities, and policymakers do to address these impacts?

Addressing these questions means delving into the complexity of population, health, and environment relationships and reaching out to experts from diverse fields. Natural and social scientists who study demographic trends, political structure, land use, agriculture, climate change, biodiversity loss, and an array of other specialties can all contribute to a greater understanding of population, health, and environment relationships.

But the synthesis of these contributions has been stymied by the very diversity of the scientific disciplines involved. Each field has its own terminology, methodology, and priorities. Fortunately, there is a growing awareness that closer cooperation among scientists from different disciplines will help head off current and impending threats to human and environmental well-being.

Translating increased knowledge into policies and action that will protect the well-being of people and the environment may be the greatest challenge of all. Researchers need to educate policymakers and the public about why they need to take action and what they can do. Researchers also must be able to justify the social, political, and economic costs of laws and policies that sometimes conflict with culture and tradition, such as expanding women’s rights, regulating land use, and requiring cleaner industrial technology. Efforts to address population, health, and environment issues extend from the global level, which requires international cooperation, to the household level, which involves individual choices and behavior.

These challenges are daunting, but there are a number of success stories to guide us. The policies that slow population growth by lowering fertility are well known, for example. Effective policies involve improving education, primary health care, and employment opportunities and raising the status of women. Laws to regulate pollution have been responsible for cleaner air and water in many countries. More efficient technology and new materials promise to reduce toxic wastes and ease the demand on natural resources.

At the community level, conservation and health organizations have cooperated on successful projects to integrate environmental protection and public health. And individuals have demonstrated a willingness to change behavior when they believe it is necessary, illustrated by a widespread compliance with recycling policies in some countries, for example. As the knowledge base, community experience, and political expertise expand, there will be many more lessons to guide the efforts to promote human and environmental well-being.

Roger-Mark De Souza is the technical director of the population, health, and environment program at the Population Reference Bureau. John S. Williams is a demographer at the Population Reference Bureau who specializes in population, environment, and community programs. Frederick A.B. Meyerson is an ecologist and demographer who specializes in population policy and the interactions between population and the environment, particularly climate change and biodiversity.